Electrochemical cell having multiplate electrodes with differing discharge rate regions

ABSTRACT

An electrochemical cell comprising a medium rate electrode region intended to be discharged under a substantially constant drain and a high rate electrode region intended to be pulse discharged, is described. Both electrode regions share a common anode and are activated with the same electrolyte.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to the conversion of chemicalenergy to electrical energy. More particularly, the present inventionrelates to an electrochemical cell dischargeable under both an constantdischarge rate and a pulse discharge rate. Cardiac defibrillatorspresent both electrical power requirements.

The constant discharge rate portion of the multiplate cell of thepresent invention, referred to hereinafter as the medium rate region,preferably includes a high mass, low surface area cathode structureassociated with an alkali metal anode in a side-by-side prismaticconfiguration. The pulse discharge rate portion of the multiplate cellof the present invention, referred to hereinafter as the high rateregion, preferably includes a high surface area cathode associated withan alkali metal anode in a side-by-side prismatic configuration.Preferably the same anode structure is electrically associated with boththe medium rate cathode region and the high rate cathode region housedwithin the same hermetically sealed casing. This structure defines whatis meant by a medium rate region and a high rate region contained withinthe same electrochemical cell.

2. Prior Art

Traditionally, cardiac defibrillator cells have been built using amultiplate electrode design. The cell designer must decide betweenproviding additional electrochemically active components for increasedmass and energy density or providing increased surface area for greaterpower density. Because of the wide disparity in the energy/powerrequirements placed upon a cardiac defibrillator cell or battery, thatbeing intermittent low rate and high rate operation, a compromise isoften decided upon. However, any design attempt to balance theenergy/power requirements placed upon the cell or battery by thedefibrillator device must not consequently produce unwantedself-discharge reactions. This compromise can provide for inefficiencyand can decrease the overall gravimetric and volumetric energy densityof the cell.

It is generally accepted that when low electrical currents are desired,the electrodes within a cell should have as much mass and as littlesurface area as possible. At the expense of power density, this providesfor increased energy density while the low electrode surface areaminimizes undesirable self-discharge reactions. Conversely, when largerelectrical discharge currents are required, electrode surface area andpower density are maximized at the expense of energy density andself-discharge rate.

The cell of the present invention having an electrode assembly withdiffering discharge rate portions fulfills this need. The present cellcomprises regions containing a low interelectrode surface area in aside-by-side, prismatic configuration, preferred for routine monitoringby a device, for example a cardiac defibrillator, and regions containinga high interelectrode surface area in a side-by-side, prismaticconfiguration for use when high rate electrical pulse charging ofcapacitors is required with minimal polarization. It is believed thatthe present electrochemical cell having multiplate electrodes withdiffering discharge rate regions represents a pioneering advancementwherein a medium discharge rate region and a high discharge rate regionare provided within the same case for the purpose of having the cellsupply at least two different electrical energy requirements.

SUMMARY OF THE INVENTION

The present invention provides an improved multiplate electrode designfor a cell dischargeable to provide background current intermittentlyinterrupted by current pulse discharge. The disclosed cell is of acase-negative design in which the anode assembly is in electricalcontact with the case. Two positive terminal pins are respectivelyconnected to two independent cathode regions. One cathode region has arelatively low surface area and high density for providing lowelectrical current on the order of microamperes to milliamperes and theother cathode region has a relatively high surface area for providinghigh electrical current on the order of several amperes.

The medium rate, constant discharge region of the present multiplatecell comprises a cathode structure of one or more cathode plates flankedon either side by an alkali metal anode. The cathode material, whichpreferably comprises a mixed metal oxide or a carbon/graphiteintercalation compound, suitable conductive additive(s) and a binder,may be in a dry powder form and is pressed onto a conductive metalscreen. The alkali metal anode is preferably a piece of lithium orlithium-alloy foil that is also pressed onto a conductive metal screen.A metallic lead connects the medium rate cathode region to a feedthroughterminal pin in the battery header which is insulated from the batterycase by a glass-to-metal seal The anode can either be connected to thecase resulting in a case-negative configuration or to anotherfeedthrough pin also located in the header of the battery. A separatorprevents short circuiting between the couple.

The high rate, pulse discharge region of the present multiplate cellcomprises a cathode structure of one or more cathode plates flanked oneither side by the same anode that is coupled to the medium rate region.The interelectrode surface area of the high rate region is greater thanthat of the medium rate region to deliver high current pulses duringdevice activation. Preferably the medium high rate region contributesgreater than 10% of the total energy density provided by the cell whilehaving less than 50% of the total cathode surface area. Still morepreferably, the medium rate region contributes greater than 10% of thetotal energy density provided by the cell while having less than 30% ofthe total cathode surface area.

Thus, the present invention offers the advantage of having both a mediumrate, constant discharge or constant drain region and a high rate, pulsedischarge region provided within the same electrochemical cell. Theelectrochemical couple used for both the medium rate region and the highrate region is, for example, an alkali metal/mixed metal oxide couplesuch as a lithium-silver vanadium oxide couple. However, both dischargeregion couples need not necessarily be identical multiplate electrodeelectrochemical cells according to the present invention having mediumrate and high rate discharge regions can be constructed/designed to meetthe drain rate and current discharge requirements of a particularapplication.

These and other aspects of the present invention will become moreapparent to those skilled in the art by reference to the followingdescription and the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of an electrochemical cell 10 withmultiplate electrodes according to the present invention

FIG. 2 is a schematic of the electrochemical cell shown in FIG. 1.

FIG. 3 is a graph constructed from the simultaneous discharge of anelectrochemical cell according to the present invention having a mediumrate, constant discharge region and a high rate, pulse discharge region.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, FIGS. 1 and 2 show an electrochemicalcell 10 with multiplate electrodes constructed according to the presentinvention having both a medium rate region 12 and a high rate region 14hermetically sealed within a metallic, prismatic casing 16. The mediumrate region 12 preferably provides a relatively constant dischargecurrent and, the high rate region 14 preferably provides a current pulsedischarge power source. Both electrode regions are activated with thesame electrolyte solution.

As diagrammatically shown in FIG. 2, the present multiplate electrodecell comprises two positive terminal leads 18, 20 and a common negativeterminal lead 22. In other words, the medium rate region and the highrate region have separate and distinct positive terminals and the samenegative terminal, i.e., the prismatic casing 16. Two different loadsare applied to this battery. A constant resistance load 24 is connectedto the positive terminal 18 and the negative terminal 20, i.e., thecasing 16, and a constant current pulse "load" 26 is connected to thepositive terminal 20 and the casing 16. The housing 16 is vacuum filledwith a nonaqueous electrolyte common to both the medium rate region 12and the high rate region 14. A device providing both a constantresistance load and a constant current pulse "load" is, for example, animplantable medical device such as a cardiac defibrillator.

More particularly, the anode electrode for the medium rate region andthe high rate region of an electrochemical cell with multiplateelectrodes according to the present invention is selected from Group IAof the Periodic Table of Elements, including lithium, sodium, potassium,calcium, magnesium or their alloys, or any alkali metal or alkali-earthmetal capable of functioning as an anode. Alloys and intermetalliccompounds include, for example, Li--Si, Li--B and Li--Si--B alloys andintermetallic compounds. The preferred anode comprises lithium, and themore preferred anode comprises a lithium alloy, the preferred lithiumalloy being lithium-aluminum with the aluminum comprising from betweenabout 0% to about 50%, by weight, of the alloy.

As shown in FIG. 1, the anode for the medium rate region 12 and the highrate region 14 is a thin metal sheet or foil 28 of the anode metal,pressed or rolled on a metallic anode current collector, i.e.,preferably comprising nickel. The anode has an extended tab or lead ofthe same material as the anode current collector, i.e., preferablynickel, integrally formed therewith, such as by welding. In thisconfiguration, the lead is contacted by a weld to the conductive metalcasing 16 serving as the negative terminal 20 in a case-negativeconfiguration for both regions 12, 14. The casing 16 is preferably aprismatic housing that may comprise materials such as stainless steel,mild steel, nickel-plated mild steel, titanium or aluminum, but notlimited thereto, so long as the metallic material is compatible for usewith the other components of the cell.

The cathode active material for both the medium rate and high rateregions may comprise a metal element, a metal oxide, a mixed metaloxide, a metal sulfide or carbonaceous compounds, and combinationsthereof. Suitable cathode active materials include silver vanadium oxide(SVO), copper vanadium oxide, copper silver vanadium oxide (CSVO),manganese dioxide, titanium disulfide, copper oxide, copper sulfide,iron sulfide, iron disulfide, lithiated cobalt oxide, lithiated nickeloxide, carbon and fluorinated carbon, and mixtures thereof.

Preferably, the cathode active material comprises a mixed metal oxideformed by a chemical addition reaction, thermal decomposition reaction,hydrothermal synthesis, sol-gel formation, chemical vapor deposition,ultrasonically generated aerosol deposition, or by a thermal spraycoating process of various metal sulfides, metal oxides or metaloxide/elemental metal combinations. The materials thereby producedcontain metals and oxides of Groups IB, IIB, IIIB, IVB, VB, VIB, VIIBand VIII of the Periodic Table of Elements, which includes the noblemetals and/or their oxide compounds.

By way of illustration, and in no way intended to be limiting, anexemplary cathode active material comprises silver vanadium oxide havingthe general formula Ag_(x) V₂ O_(y) in any one of its many phases, i.e.,β-phase silver vanadium oxide having in the general formula x=0.35 andy=5.18, γ-phase silver vanadium oxide having in the general formulax=0.74 and y=5.37 and ε-phase silver vanadium oxide having in thegeneral formula x=1.0 and y=5.5, and combination and mixtures of phasesthereof.

In the case of the cathode structure for the medium rate region 12, thecathode active material may be in a dry powder form and pressed onto aconductive metal screen. Suitable materials for the cathode currentcollector include aluminum and titanium, preferably titanium.Preferably, prior to contact with the conductive current collector, thecathode active material in a finely divided form is mixed withconductive diluents and a binder material and then pressed onto thecurrent collector screen. The binder material is preferably athermoplastic polymeric binder material. The term thermoplasticpolymeric binder material is used in its broad sense and any polymericmaterial which is inert in the cell and which passes through athermoplastic state, whether or not it finally sets or cures, isincluded within the term "thermoplastic polymer". Representativematerials include polyethylene, polypropylene and fluoropolymers such asfluorinated ethylene and fluorinated propylene, polyvinylidene fluoride(PVDF) and polytetrafluoroethylene (PTFE), the latter material beingmost preferred. Natural rubbers are also useful as the binder materialwith the present invention.

Suitable discharge promoter diluents include graphite powder, acetyleneblack powder and carbon black powder. Metallic powders such as nickel,aluminum, titanium and stainless steel in powder form are also useful asconductive diluents. In practice, about 80% to about 98%, by weight, ofthe cathode active material is mixed with about 1% to about 5% of theconductive diluents and, about 1% to about 5% of the binder material. Insome cases, no binder material or electronic conductor material isrequired to provide a similarly suitable cathode body. The cathodestructure for the medium rate region may also be prepared by rolling,spreading or pressing a mixture of the materials mentioned above onto asuitable current collector.

The cathode structure for the medium rate region 12, prepared asdescribed above, is preferably in the form of one or more cathode plates30 operatively associated with the previously described anode sheet 28.The cathode plates 30 have a relatively low surface area and highdensity for providing low electrical current on the order of about 1microampere to about 100 milliamperes. Preferably, at least one cathodeplate 30 having a thickness of about 0.004 inches to about 0.040 inchesis flanked on either side by oppositely positioned surfaces of the anode28 prepared as described above

The high rate region 14 of the present cell comprises cathode plates 32formed from a paste of cathode active material, including binder andconductive additives, calendared into a free-standing structure that issubsequently dried and cut to shape. The shaped cathode structure havinga thickness of about 0.001 inches to about 0.025 inches is then pressedonto at least one side and preferably both sides of a current collectorscreen of a suitable material, such as aluminum or titanium withtitanium being preferred, to provide the cathode structure in the formof plates 32. Preferably, at least one cathode plate 32 is flanked oneither side by oppositely positioned surfaces of the anode 28 not facingthe cathode plates 30 of the medium rate section 12 to provideelectrical current on the order of about 1 amp to about 4 amps for thehigh rate region. A process for making cathode structures useful in thehigh rate region of the present multiplate electrode cell is describedin U.S. Pat. No. 5,435,874 to Takeuchi et al., which is assigned to theassignee of the present invention and incorporated herein by reference.An alternate preparation technique is to cast a slurry of the cathodeactive material onto a surface-treated metal foil followed by drying andcalendaring.

The lead 18 for the cathode plates 30 of the medium rate region 12 andthe lead 20 for the cathode plates 32 of the high rate region 14 areinsulated from the casing 16 by respective glass-to-metal seal/terminallead feedthroughs. The glass used is of a corrosion resistant typehaving from between about 0% to about 50% by weight silicon such asCABAL 12, TA 23, CORNING 9013, FUSITE 425 or FUSITE 435. The positiveterminal leads 18, 20 preferably comprise molybdenum although titanium,aluminum, nickel alloy, or stainless steel can also be used.

The cathode plates 30, 32 and the anode sheet 28 for both the mediumrate and high rate regions are preferably sealed in their own separatorenvelopes (not shown for clarity) to prevent direct physical contactbetween them. The separators are of an electrically insulative materialto prevent an internal electrical short circuit between the activematerials, and the separator material also is chemically unreactive withthe anode and cathode active materials and both chemically unreactivewith and insoluble in the electrolyte. In addition, the separatormaterial has a degree of porosity sufficient to allow flow therethroughof the electrolyte during the electrochemical reaction of the cell.Illustrative separator materials include woven and non-woven fabrics ofpolyolefinic fibers including polypropylene and polyethylene orfluoropolymeric fibers including polyvinylidine fluoride,polyethylenetetrafluoroethylene, and polyethylenechlorotrifluoroethylenelaminated or superposed with a polyolefinic or fluoropolymericmicroporous film, non-woven glass, glass fiber materials and, ceramicmaterials. Suitable microporous films include a polytetrafluoroethylenemembrane commercially available under the designation ZITEX (ChemplastInc.), a polypropylene membrane commercially available under thedesignation CELGARD (Celanese Plastic Company, Inc.) and a membranecommercially available under the designation DEXIGLAS (C.H. Dexter,Div., Dexter Corp.).

The multiplate electrochemical cell of the present invention furtherincludes a nonaqueous, ionically conductive electrolyte which serves asa medium for migration of ions between the anode and the cathodestructures during the electrochemical reactions of the cell. Theelectrochemical reaction at both the medium rate and high rate regionsinvolves conversion of ions in atomic or molecular forms which migratefrom the anode to the cathode. Thus, nonaqueous electrolytes suitablefor the present invention are substantially inert to the anode andcathode materials and, they exhibit those physical properties necessaryfor ionic transport namely, low viscosity, low surface tension andwettability.

A suitable electrolyte has an inorganic, tonically conductive saltdissolved in a nonaqueous solvent, and more preferably, the electrolyteincludes an ionizable alkali metal salt dissolved in a mixture ofaprotic organic solvents comprising a low viscosity solvent and a highpermittivity solvent. The inorganic, ionically conductive salt serves asthe vehicle for migration of the anode ions to intercalate into thecathode active material, and has the general formula MM'F₆ wherein M isan alkali metal similar to the alkali metal comprising the anode and M'is an element selected from the group consisting of phosphorous, arsenicand antimony. Examples of salts yielding M'F₆ are: hexafluorophosphate(PF₆), hexafluoroarsenate (AsF₆) and hexafluoroantimonate (SbF₆), whiletetrafluoroborate (BF₄) is exemplary of salts yielding M'F₄.Alternatively, the corresponding sodium or potassium salts may be used.

Preferably the electrolyte comprises at least one ion-forming alkalimetal salt of hexafluorophosphate, hexafluoroarsenate orhexafluoroantimonate dissolved in a suitable organic solvent wherein theion-forming alkali metal of the salt is similar to the alkali metalcomprising the anode. Thus, in the case of an anode comprising lithium,the alkali metal salt comprises lithium hexafluorophosphate, lithiumhexafluoroarsenate or lithium hexafluoroantimonate dissolved in asuitable solvent mixture. Other inorganic salts useful with the presentinvention include LiBF₄, LiCl0₄, Li₂ 0, LiAlCl₄, LiGaCl₄, LiC(SO₂ CF₃)₃,LIN(SO₂ CF₃)₂ and LiCF₃ SO₃, and mixtures thereof.

Low viscosity solvents include tetrahydrofuran (THF), methyl acetate(MA), diglyme, triglyme, tetraglyme, dimethyl carbonate (DMC), ethylmethyl carbonate (EMC) diethyl carbonate and 1,2-dimethoxyethane (DME),and mixtures thereof, and high permittivity solvents include cycliccarbonates, cyclic esters and cyclic amides such as propylene carbonate(PC), ethylene carbonate (EC), acetonitrile, dimethyl sulfoxide,dimethyl formamide, dimethyl acetamide, γ-butyrolacetone (GBL) andN-methyl-pyrrolidinone (NMP), and mixtures thereof. In the presentinvention, the anode is lithium metal and the preferred electrolyte is1.0M to 1.4M LiAsF₆ dissolved in an aprotic solvent mixture comprising a50/50 mixture (by volume) of propylene carbonate (PC) anddimethoxyethane (DME).

The casing header comprises a metallic lid (not shown) having asufficient number of openings to accommodate the glass-to-metalseal/terminal lead feedthroughs for the cathode plates 30, 32 of themedium and high rate regions 12,14. An additional opening is providedfor electrolyte filling. The casing header comprises elements havingcompatibility with the other components of the electrochemical cells andis resistant to corrosion. The cell is thereafter filled with theelectrolyte solution described hereinabove and hermetically sealed suchas by close-welding a stainless steel plug over the fill hole, but notlimited thereto

An exemplary electrochemical cell dischargeable under both a constantdischarge rate and a pulse discharge rate according to the presentinvention may be constructed having a capacity (Qa) of the anode and acapacity (Qc) of the high rate region and of the medium rate region asfollows:

1) A first exemplary condition consists of the high rate region and themedium rate region each having a Qa:Qc ratio greater than 0.8:1.0. Thisprovides the cell of the present invention with adequate anode capacity(Qa) associated with both the high rate region and the medium rateregion dischargeable through both the first and second voltage plateausexpected in the discharge of a conventional Li/SVO cell. In the presentcell, the Qa:Qc capacity ratio for both the medium rate and high rateregions may be as high as 1.1:1.0 or as low as 0.8:1.0 to control cellswelling.

2) A second exemplary condition consists of the high rate region of thecell of the present invention having a significantly lower Qa:Qc thatthe medium rate region. For example, the Qa:Qc for the high rate regionmay be as low as 0.4:1.0 while the anode capacity to cathode capacityfor the medium rate region is about 1.1:1.0.

The overall cell balance depends on the ratio of capacity for the highrate region to the medium rate region of the cell. Preferably the highrate region is less than 50% of the total cell capacity, while themedium rate region comprises greater than 50% of the total cellcapacity. In the case of a 50:50 capacity ratio between the high rateand medium rate regions of the total cell capacity, the respective Qa:Qcratios are shown in Table 1.

                  TABLE 1    ______________________________________    High Rate    Medium Rate Total Cell    Region (Qa:Qc)                 Region (Qa:Qc)                             Capacity (Qa:Qc)    ______________________________________    0.4:1.0      1.1:1.0     0.75:1.0    ______________________________________

In the case where the capacity ratio of the medium rate region to thehigh rate region is 0.6:0.4, the respective Qa:Qc rations are shown inTable 2.

                  TABLE 2    ______________________________________    High Rate    Medium Rate Total Cell    Region (Qa:Qc)                 Region (Qa:Qc)                             Capacity (Qa:Qc)    ______________________________________     0.4:1.0!     1.1:1.0!   0.82:1.0    40% of total 60% of total    cathode capacity                 cathode capacity    ______________________________________

The following examples describe the manner and process of anelectrochemical cell having multiplate electrodes according to thepresent invention, and they set forth the best mode contemplated by theinventors of carrying out the invention, but they are not to beconstrued as limiting.

EXAMPLE I

Nine lithium/silver vanadium oxide (Li/SVO) defibrillator cells werebuilt The cathode of each cell comprised a dry mix of SVO combined witha binder material and a conductive diluent pressed into six plates Thecasing header contained two terminal pins for connection to the cathodeSpecifically, five of six cathode plates were electronically connectedto each other and welded to the first terminal pin to provide a highrate discharge region. The remaining cathode plate was welded to thesecond terminal pin to form a medium rate electrode region. The cellswere activated with an electrolyte of LiAsF₆ dissolved in a 50:50mixture, by volume, of propylene carbonate and dimethoxyethane.

Two of the experimental cells were submitted for short circuit testingat 37° C. using a circuit resistance less than or equal to tenmilliohms. The two cells exhibited a peak current of 16.7 amps and 17.2amps, respectively, within one second of application of the shortcircuit. One cell exhibited a peak temperature of 118.0° C. at 9:18(minutes:seconds) into the test. The other cell exhibited a peaktemperature of 115.0° C. at 10:30 (minutes:seconds) into the test. Bothcells exhibited case swelling. Neither cell was observed to leak, ventor rupture.

The remaining seven cells were subjected to burn-in and acceptance pulsetesting and then subjected to a modified accelerated discharge data(ADD) test. Based on electrode surface area, the electrical testparameters were modified so that the same current density was applied tothe cells during various aspects of the test. For burn-in and acceptancepulse testing, the two terminal pins were electrically connected and thecells were subjected to a burn-in load of 2.49 kohm for 17 hours. Themean pre-load open current volting (OCV) and post-load OCV of the cellsduring burn-in was 3.477 volts and 3.200 volts, respectively. Duringacceptance pulse test, the mean pre-pulse OCV was 3.266 volts. The cellswere then subjected to a 2.0 amp acceptance pulse test at 37° C. A pulsetrain sequence of four pulses each of ten seconds duration with fifteenseconds of rest between pulses was used. During acceptance pulsetesting, the mean pre-pulse OCV was 3.266 volts. The average P1 edgevoltage, P1 minimum voltage, P1 end voltage, P4 minimum voltage and postpulse voltage during acceptance pulse testing was 2.669 volts, 2.404volts, 2.606 volts, 2.559 volts, and 3.083 volts, respectively.Following acceptance pulse testing, the external electrical connectionbetween the two terminal pins was removed

The seven cells were then submitted for continuous discharge and pulsetesting. During this test, the terminal pin connected to the singlecathode plate of the medium rate discharge region was connected to a17.4 kohm resistor. This cathode plate continuously supplied abackground current for the cell throughout the test. Once every week, a1.7 amp pulse train of four pulses of ten seconds duration with fifteenseconds of rest between pulses was applied to the other terminal pinconnected to the five cathode plates of the high rate discharge region.All tests were conducted at 37° C.

The background voltage of the continuous discharge and pulse dischargetested cells exhibited the characteristic SVO discharge profile andseveral voltage plateaus were observed. The individual cells providedthirty-eight pulse trains through one of the terminal pins as thebackground voltage through the other terminal pin declined toapproximately 750 millivolts. Despite the low background voltage, thepulse 4 minimum voltage of the cells remained above 2.0 volts and thepre-pulse OCV of the electrode assembly designated for high rate pulsingremained above 2.70 volts. The discharge profile, voltage response andcapacity provided by the seven cells was similar.

FIG. 3 is a graph constructed from the simultaneous continuous dischargeand pulse discharge of a representative one of the group of seven cells.In particular, curve 100 was constructed from the background current ofthe medium rate, constant discharge region of the present invention celland, curve 102 was constructed from the open circuit voltage of the highrate, pulse discharge region, curve 104 was constructed from the pulse 1minimum voltage and curve 106 was constructed from the pulse 4 minimumvoltage of the pulse discharge region.

These results demonstrate that an Li/SVO defibrillator cell can bedesigned in such a manner so as to provide a higher pulse voltage whenthe background voltage is low. The design of such a cell is specific toeach application and a reasonable compromise must be made among thedesign variables.

It is appreciated that various modifications to the inventive conceptsdescribed herein may be apparent to those skilled in the art withoutdeparting from the spirit and scope of the present invention defined bythe hereinafter appended claims.

What is claimed is:
 1. An electrochemical cell, which comprises:(a) afirst electrode provided in a folded, accordion pleated shape andcomprising a first electrode active material; (b) a second electrodeelectrically associated with the first electrode to provide at least afirst region and a second region of the cell, wherein the first regionand the second region of the cell are provided by respective first andsecond structures of the second electrode disposed between the folds ofthe first electrode with at least a portion of the first electrode in aface-to-face relationship with at least one side of each of the firstand second structures of the second electrode; and (c) an electrolyteactivating and operatively associating the first electrode and secondelectrode such that the first region and the second region aredischargeable independent of each other to provide separate andindependent sources of electrical energy.
 2. The electrochemical cell ofclaim 1 wherein the first region contributes greater than 10% of thetotal energy density of the cell while the first structure provides lessthan 50% of the total surface area provided by the second electrode. 3.The electrochemical cell of claim 1 wherein the first electrode is theanode and the second electrode is the cathode.
 4. The electrochemicalcell of claim 1 wherein the first region of the cell has greater than10% of the total energy density of the cell while the first structureprovides less than 30% of the total, surface area.
 5. Theelectrochemical cell of claim 1 including a conductive casing serving asa terminal for the first electrode and wherein the first structure ofthe second electrode is connected to a first terminal lead and thesecond structure of the second electrode is connected to a secondterminal lead.
 6. The electrochemical cell of claim 1 wherein the firstelectrode is a lithium anode and the second electrode is a silvervanadium oxide cathode and the first region of the cell is dischargeableat a relatively low electrical current of about 1 microampere, to about100 milliamperes corresponding to a C-rate of about C/2,300,000 to aboutC/23 , and wherein the second region of the cell is dischargeable at arelatively high electrical current of about 1 ampere to about 4 amperescorresponding to a C-rate of about C/2.3 to about C/0.575.
 7. Theelectrochemical cell of claim 1 wherein the first electrode is a lithiumanode and the second electrode is a silver vanadium oxide cathode andthe first region and the second region each contribute about 50% of thetotal cell capacity and a ratio of a capacity (Qa) of the firstelectrode to a capacity (Qc) of the second electrode is greater thanabout 0.75:1.0.
 8. The electrochemical cell of claim 1 wherein a ratioof a capacity of the first electrode to a capacity of the secondelectrode in the first region of the cell is about 1.1:1.0.
 9. Theelectrochemical cell of claim 1 wherein a ratio of a capacity of thefirst electrode to a capacity of the second electrode in the secondregion of the cell is about 0.4:1.0.
 10. The electrochemical cell ofclaim 1 wherein a capacity ratio of the first region to the secondregion is about 0.6:0.4.
 11. The electrochemical cell of claim 10wherein a ratio of a capacity of the first electrode to a capacity ofthe second electrode in the second region of the cell is about 0.4:1.0,and wherein a ratio of the capacity of the first electrode to thecapacity of the second electrode in the first region is about 1.1:1.0.12. The electrochemical cell of claim 1 wherein the first structure ofthe second electrode is provided at least in part by a second electrodeactive material and wherein the second structure of the second electrodeis provided at least in part by a third electrode active material. 13.The electrochemical cell of claim 12 wherein the second and thirdelectrode active materials are the same.
 14. The electrochemical cell ofclaim 12 wherein the second and third electrode active materials aredissimilar.
 15. The electrochemical cell of claim 1 wherein the firstand second structures comprise respective first and second plates havingopposed major surfaces disposed between the folds of the first electrodesuch that a portion of the first electrode is in a face-to-facerelationship with the opposed major surfaces of both the first andsecond plates to provide the respective first and second regions of thecell.
 16. The electrochemical cell of claim 1 wherein the firstelectrode is an anode and wherein the first region of the cell comprisesa first cathode of a first cathode active material electricallyassociated with the anode and the second region of the cell comprises asecond cathode of a second cathode active material electricallyassociated with the anode.
 17. The electrochemical cell of claim 16wherein the anode and the associated first cathode provide electricalenergy at a first current and wherein the anode and the associatedsecond cathode provide electrical energy at a second current greaterthan the first current.
 18. The electrochemical cell of claim 16 whereinthe anode associated with the first cathode is dischargeable under asubstantially constant discharge rate and the anode associated with thesecond cathode is dischargeable under a current pulse dischargeapplication.
 19. The electrochemical cell of claim 16 wherein the anodeis comprised of lithium.
 20. The electrochemical cell of claim 16wherein the anode comprises a lithium-aluminum alloy.
 21. Theelectrochemical cell of claim 20 wherein aluminum comprises from betweenabout 0% to about 50% by weight of the anode alloy.
 22. Theelectrochemical cell of claim 16 wherein the first and second cathodeactive materials are the same.
 23. The electrochemical cell of claim 16wherein the first and second cathode active materials are dissimilar.24. The electrochemical cell of claim 16 wherein the first and secondcathode active materials of the first and second cathodes are selectedfrom the group consisting of silver vanadium oxide, copper silvervanadium oxide, manganese dioxide, cobalt oxide, nickel oxide, copperoxide, titanium disulfide, copper sulfide, iron sulfide, iron disulfidecopper vanadium oxide, carbon and fluorinated carbon and mixturesthereof.
 25. The electrochemical cell of claim 16 wherein at least oneof the first and second cathodes comprises a calendared mixed metaloxide.
 26. The electrochemical cell of claim 16 wherein the first andsecond cathode active materials of the first and second cathodes bothcomprise a mixed metal oxide formed as a preparation product of one ofthe group consisting of a thermal treatment reaction, addition reaction,sol gel formation, chemical vapor deposition, ultrasonically generatedaerosol deposition and hydrothermal synthesis of vanadium oxide and asecond metal.
 27. The electrochemical cell of claim 16 wherein both thefirst and second cathodes comprise from between about 80 weight percentto about 99 weight percent of the cathode active material.
 28. Theelectrochemical cell of claim 16 wherein at least one of the first andsecond cathodes further comprises a binder material and conductiveadditives.
 29. The electrochemical cell of claim 28 wherein the bindermaterial is a thermoplastic material.
 30. The electrochemical cell ofclaim 28 wherein the conductive additives are selected from the groupconsisting of carbon, graphite powder, acetylene black and metallicpowders including nickel, aluminum, titanium and stainless steel, andmixtures thereof.
 31. The electrochemical cell of claim 16 wherein thefirst and second cathodes comprise about 1 to 5 weight percent of aconductive additive, about 1 to 5 weight percent of a binder materialand about 80 to 99 weight percent of a cathode active material.
 32. Theelectrochemical cell of claim 16 wherein the first and second cathodesare in the form of plates having a thickness in the range of from about0.001 inches to about 0.040 inches.
 33. The electrochemical cell ofclaim 16 wherein a casing houses the anode and the associated firstcathode as a first electrochemical couple dischargeable under asubstantially constant discharge application, the first couplecomprising:i) the anode comprising alkali metal; and ii) the firstcathode active material of the first cathode selected from the groupconsisting of a metal, a metal oxide, a mixed metal oxide, a metalsulfide and a carbonaceous compound, and mixtures thereof;and whereinthe casing further houses the anode and the associated second cathode asa second electrochemical couple dischargeable under a current pulsedischarge application, the second couple comprising: i) the anode; andii) the second cathode active material of the second cathode selectedfrom the group consisting of a metal, a metal oxide and a mixed metaloxide, a metal sulfide and a carbonaceous compound, and mixturesthereof.
 34. The electrochemical cell of claim 33 wherein the anode iselectrically connected to the casing to provide a case-negativeconfiguration for the cell.
 35. The electrochemical cell of claim 33wherein both the first and second cathodes are electrically connected torespective cathodes terminals electrically insulated from the casing.36. The electrochemical cell of claim 33 wherein the electrolytesolution operatively associated with both the first and secondelectrochemical couples comprises an inorganic salt having the generalformula MM'F₆ dissolved in a nonaqueous solvent, wherein M is an alkalimetal similar to the alkali metal comprising the anode and the M' is anelement selected from the group consisting of phosphorous, arsenic andantimony.
 37. The electrochemical cell of claim 36 wherein the alkalimetal of the anode comprises lithium and the inorganic salt comprisingthe electrolyte solution is lithium hexafluoroarsenate.
 38. Theelectrochemical cell of claim 36 wherein the nonaqueous solventcomprises an organic solvent selected from the group consisting oftetrahydrofuran, dimethyl carbonate, ethyl methyl carbonate, diethylcarbonate, propylene carbonate, methyl acetate, acetonitrile, dimethylsulfoxide, dimethyl formamide, dimethyl acetamide, ethylene carbonate,diglyme, triglyme, tetraglyme, 1,2-dimethoxyethane γ-butyrolactone andN-methyl-pyrrolidinone, and mixtures thereof.
 39. The electrochemicalcell of claim 36 wherein the nonaqueous solvent is an organic solventthat comprises propylene carbonate and dimethoxyethane.
 40. Theelectrochemical cell of claim 39 wherein the propylene carbonate anddimethoxyethane are present in a ratio of about 1:1, by volume.
 41. Theelectrochemical cell of claim 33 wherein the first electrochemicalcouple comprises portions of the anode disposed adjacent to oppositesides of the first cathode and wherein the second electrochemical couplecomprises portions of the anode disposed adjacent to opposed sides ofthe second cathode.
 42. The electrochemical cell of claim 33 wherein theanode is comprised of lithium.